Kinkly explains Diaper Fetishism

Diaper fetishism is associated with infantilism and child-like fantasies. For some individuals it is only the thought of wearing a diaper, or the thought of someone else wearing a diaper that causes sexual arousal, while for others it is the infant/caretaker role-play that stimulates excitation. For some individuals it is messing (urinating or defecating) in a diaper that is the source of arousal.

Diaper fetishism can also be used within the context of BDSM activity, where the diaper is used as a source of humiliation.